1. Field of the Invention
The present invention relates to spent fuel shipping containers for nuclear fuel removed from a reactor and, more particularly, to device and method loading such containers with spent fuel.
2. The Prior Art
A spent fuel shipping container is a large steel cylinder or drum, typically 8 ft. in diameter and 15 ft. in height, and weighing 300,000 lbs. The container is used for the shipment of multiple pieces of spent nuclear fuel. Referring to FIG. 1, a representative container, which is generally denoted 10, includes a top or lid 12 that can be rotated on a bearing (not shown) such that an access opening 14 in the top of the container, i.e., in the cover 12, can be rotated to a position wherein the opening 14 is positioned precisely over the center of one of a plurality of fuel pockets 16 provided within container 10. Thus, spent fuel is inserted through access opening 14 into container 10 and thence into the selected fuel pocket 16. An index ring (not shown in FIG. 1), graduated in degrees, is affixed to the top 12 of the container 10 so that the correct indexed location of the access opening 14 over each of the respective pockets 16 can be identified for recording.
Prior to placing fuel inside the container 10, the precise index location of each pocket 16 is determined by the use of a mechanical alignment device (not shown). Typically, this alignment device is shaped like a cylindrical "plug" with a rod extending vertically upwardly through the top of the plug. The plug is inserted through the access opening 14 of the cover 12 into the corresponding container pocket 16. The diameter of the plug is such that the plug forms what is effectively a piston--cylinder fit with the pocket 16. Once the plug is installed, the rod associated with the plug, which extends upwardly above the top of container 10, is used, along with suitable mechanical adapters, to establish that the center of the access opening 14 is precisely aligned with the center of the corresponding fuel pocket 16. The reading of the index ring (in degrees of rotation) is then recorded and this reading is used subsequently to align the opening 14 in the cover 12 in the appropriate position above each of the other fuel pockets 16 as fuel is put into the container.
It will be appreciated that the mechanical alignment device described above suffers a number of disadvantages and limitations. Some disadvantages of the prior art mechanical device and the method of using the same include those resulting from the fact that the mechanical device must be installed into, and in contact with, the "internals" of the spent fuel container which are highly radioactively contaminated. Thus, during the alignment operation, the radioactive contamination is transferred to the alignment device itself. After alignment of each fuel pocket, the alignment device is removed and must be partially decontaminated prior to the installation thereof into the next pocket. After the completion of all alignments, the device is completely decontaminated for subsequent packaging and storage until the next container is prepared for use. It will be appreciated that this radioactive decontamination presents a risk to operators due to the high levels of contamination normally encountered.
Considering other limitations and disadvantages thereof, the mechanical alignment device must be installed into and subsequently removed from, each pocket being aligned. Further, the device requires the repeated use of containments in order to be able to operate the device in a radioactive environment, i.e., so as to separate the operator from the contamination within in the container. Moreover, the required decontamination of the mechanical device subjects operating personnel to radiation exposure.
Historically, the time required to accomplish the alignment of each fuel pocket using the prior art mechanical device ranges from two to eight hours. Moreover, significant amount of time and resources are devoted to preparation of the mechanical device for use, including the performance of load testing and non-destructive testing of lifting attachments. Further, the mechanical device requires the use of an auxiliary crane for installation and removal and the device itself is inherently large and awkward to handle.